1. Field of the Invention
The present invention relates to an optical transmitting module and an optical transmitting device.
2. Description of Related Art
In an optical source of an optical transmitting module for middle and long distances having a communication rate of 2.5 Gbit/s or greater, an optical transmitting module known as an EA integrated LD in which an electro-absorptive modulator (EA) and a semiconductor laser element (LD) are equipped is widely in use. In such an optical transmitting module, a high-frequency signal is supplied to the electro-absorptive modulator so that constant and stable light which is output from the semiconductor laser element is quickly modulated and a light signal is output.
In such an optical transmitting module, there is a rising desire to employ a coaxial package which can be easily manufactured with low cost. However, because such an optical transmitting module is easily affected by a change in temperature, a constant temperature control has been necessary in order to prevent degradation of the optical output intensity and the high-speed response characteristic due to the temperature change. For this purpose, a temperature control element having high power consumption must be provided in the optical transmitting module. In order to secure the equipping space of the temperature control element, in such an optical transmitting module, in the related art, a butterfly type optical transmitting package as disclosed in JP 3330451 in FIGS. 6(1) and 22 is mainly used.
In recent years, as disclosed in “Optical Fiber Communication Conference 2005, PDP14, 200”, an EA integrated LD which does not require the constant temperature control has been introduced. With this structure, the equipping of the temperature control element in the optical transmitting package became no longer necessary. In addition, because there is a growing demand for reducing the size of the optical transmission and reception devices, receptacle type optical transmission and reception devices having an optical connecter as an interface are becoming more popular in place of pigtail type optical transmission and reception devices having an optical fiber as an interface. In receptacle type optical transmission and reception devices, because a mechanical stress is directly applied to the optical transmitting module during insertion and disconnection of the optical fiber, there is a concern that the reliability of a solder connection between a lead terminal of the optical transmitting module and a pad portion of a circuit board inside the optical transmission and reception devices may be significantly reduced. In order to avoid this, a flexible board is more widely used having a characteristic that an electrical line is formed with a conductor film formed over a base film on a connection portion of these elements, that the board can be repeatedly deformed because of its flexibility, and that the electrical characteristic is maintained even when the flexible board is deformed. In a multisource agreement for small size module of 10 Gbit/s (XMD-MSA) targeted to achieve common electrical, optical, and external shape specifications of the optical transmitting module and the optical receiving module, the use of the flexible board is set as a common specification.
As shown in FIG. 11 which is an equivalent circuit diagram of an optical transmitting module 10 having an optical modulator unit 24 such as an electro-absorptive modulator, in the optical transmitting module 10 having the optical modulator unit 24, a signal leaking from the optical modulator unit 24, that is, a signal which is output from the optical modulator 24, may reach a semiconductor laser element 23, and the waveform of the light which is output from the semiconductor laser element 23 may be disturbed.
FIG. 12 is a diagram showing an example frequency response characteristic of the optical transmitting module 10 shown in the equivalent circuit diagram of FIG. 11. FIG. 13 is a diagram showing an example optical output waveform of the optical transmitting module 10 shown in the equivalent circuit diagram of FIG. 11. As shown in FIG. 12, in the optical transmitting module 10 of the equivalent circuit diagram of FIG. 11, several dips 90 appear in a band of few GHz. Because of these dips 90, as shown in FIG. 13, an eye-aperture of the optical output waveform is degraded.
JP 3330451 discloses a technique in which a layered capacitor is equipped in an optical transmitting package in an optical transmitting module having a butterfly type optical transmitting package so that the influence of the signal which is output from the optical modulator unit on the semiconductor laser element is reduced. With the use of such a technique, the waveform of the light which is output from the semiconductor laser element can be stabilized.